1. Field of the Invention
The present invention relates to a method for cleaning a nozzle of printing apparatus, and more particularly relates to a method for cleaning a nozzle of line type inkjet printer.
2. Description of the Related Art
In an inkjet printer for color printing, nozzle arrays for ink ejection of each color; Y (yellow) color, M (magenta) color, C (cyan) color, and K (black) color, are provided. The number of times of ink jet work operations of each nozzle differs depending on patterns, hue, and density of a print image to be expressed. Accordingly, in a case of a nozzle whose number of times of ink jet work operations is few, the ink in a nozzle part is left in a stationary state for a long time, the ink is affected by a drying effect as a result of peripheral temperature and the ink agglutinates. As a result, in the worst case, the nozzle may become clogged with ink. Particularly, because the ink is not ejected from the clogged nozzle, a non-printed line may be formed and such a defective state (irreparable state) may extend to a large number of substrates.
In inkjet printers, there are two types of inkjet printers; a serial type and a line type. In the serial type printer, all nozzles provided on a print head move on a main scanning line. Accordingly, it is possible to reduce unevenness of the number of times of ink jet work operations among each nozzle by changing combinations of the nozzles to be used in one printing. For example, in Japanese Unexamined Patent Application Publication No. 2002-240257, a method that a nozzle which does not eject ink at all is detected and in subsequent printing, in order to actively use the nozzle, combinations of nozzles to be used are changed, is disclosed.
On the other hand, in the line type printer, print head of each color is fixed and printing is performed when a substrate passes right under print head of each color. Because each nozzle on a print head of each color is in charge of one print line to be formed on the substrate which passes right under the nozzle, it is not possible to change to another nozzle. Accordingly, depending on a print image to be expressed, the number of times of ink jet work operations of each nozzle is fixed. As a result, unevenness of the number of times of ink jet work operations among each nozzle is not corrected and in the extreme case, a nozzle which does not eject ink at all can exist. In such a case, in the nozzle, the nozzle can become clogged with ink. Accordingly, particularly in the line type printer, it is necessary to frequently clean the nozzle during the processing.
For example, in Japanese Unexamined Patent Application Publication No. 11-078055, a method for cleaning a nozzle of a printer is disclosed. In the method, by using a non-printing period, to all nozzles, operation of flushing in which a printing operation of n dots and a subsequent non-printing operation of m dots are repeated a predetermined number of times is performed.
As described above, in the line type printer, the possibility of clogging a nozzle is much greater than that in the serial type printer. Accordingly, by frequently cleaning the nozzle during the non-printing period, it can be possible to reduce the possibility of the clogging of a nozzle.
In the method for cleaning a nozzle of a printing apparatus in the above patent literature 2, because the same operation of flushing is performed to all nozzles, it may be suitable for a case that the number of times of ink jet work operations among each of the nozzles is relatively even such as the serial type printer. However, in a case that the line type printer is used, when the number of times of ink jet work operations among each of the nozzles is extremely uneven, the ink may be consumed more than necessary for the processing of flushing, the expensive ink is consumed, and it is extremely wasteful.